Concorde LTN-51 Reference-Frame Analysis

Abstract

Concorde routinely operated at cruise altitudes of 50 000-60 000 ft. Its sole continuous highprecision position and attitude measurements were produced by three independent Litton LTN-51 Inertial Navigation Systems (ARINC 561). These systems do not deliver model-free observations. From the first second of alignment they require mandatory insertion of present position, apply Earth-rate compensation calculated from that latitude, and maintain Schuler tuning based on an assumed Earth radius. A NASA technical paper that used a production-family LTN-51 states that the internal calculations assume a spheroidal Earth with flattening ratio 1:297 and a Schuler period of 84.4 minutes. Official British Airways limitations further restrict alignment to latitudes ≤ 76° and require the aircraft to remain stationary during the ALIGN mode. Visual horizon reports remain qualitative and uncalibrated. This paper identifies the actual airborne measurements, documents every reference-frame insertion, and treats the ellipsoidal and rotational parameters as imposed computational constructs rather than independent physical observations.